1. Field of the Invention
The present invention relates to a defect repair device and a defect repair method.
2. Discussion of the Background
In manufacturing semiconductor integrated circuits, an exposure tool is used to print fine circuit patterns on a reticle onto a wafer. In order to achieve higher integration and greater performance, integrated circuits are made to have even finer structures, and thus an exposure tool is required to print detailed circuit patterns on the wafer, obtaining a deep focal depth and high resolution. Accordingly, the use of exposure light with shorter wavelengths has been attempted. For example, exposure techniques using g-line, i-line, KrF excimer laser and ArF excimer laser have been developed, and their wavelengths are 436 nm, 365 nm, 248 nm and 193 nm, respectively. Among the light with even shorter wavelengths, there is extreme ultraviolet light (hereinafter, “EUV light”) having a wavelength of about 13.4 nm.
The exposure tool utilizing the light with a longer wavelength such as ArF laser is provided with a set of lens that transmits and refracts the exposure light to form the desired pattern on the wafer. On the other hand, in extreme ultraviolet lithography (hereinafter, “EUVL”) using EUV light for exposure, since the EUV light does not pass through any material that can be used in transmissive lens, the exposure tool is equipped with reflective mirrors that reflect the EUV light and guide the light to the wafer. In case of the reflective mirror including a multi-layer film (hereinafter, “ML film”) formed on a substrate, it is desirable to use a reflective mirror having an ML film with a completely flat surface in order to achieve a precise control of amplitude and phase of the reflected EUV light, and no defects that would degrade the imaging quality in the pattern transfer of the exposure tool is tolerated on the reflective mirror. For example, according to Evaluation of the Capability of a Multibeam Confocal Inspection System for Inspection of EUVL Mask Blanks by Stivers et al., Proceedings of SPIE Vol. 4889, p. 408, (2002), in case of manufacturing a semiconductor integrated circuit with a feature size of 32 nm, a surface bump on the ML film having a height of 2 nm and a full width at half maximum of 60 nm becomes a critical defect in the manufactured semiconductor integrated circuit. Therefore, any defects caused by deformation or disruption in the layer structure of the ML film should be effectively repaired.
Among defects of a reticle or reflective mirrors, a phase defect is a type of defect that produces a modulation of the phase of the reflected field and is caused by the displacement of layers of the ML film due to the presence of a foreign object. A method of repairing such a phase defect is disclosed in EUVL mask blank repair by Barty et al., Proceedings of SPIE Vol. 4688, p. 385, (2002) (hereinafter, “Barty et al.”). According to Barty et al., the portion around the phase defect is irradiated with an electron beam from the front surface of the ML film. However, since the ML film absorbs the electron beam to some extent, and optical properties of the ML film are controlled by about 20 to 30 layers from the front surface of the ML film, the Barty et al. technique applying the electron beam from the front surface may degrade the optical properties of the ML film.